Switching power supply device

ABSTRACT

A switching power supply device includes first to fourth switches sequentially connected in series, an inductor, a first capacitor whose first end is connected to a connection node of the first switch and the second switch and whose second end is connected to a connection node of the third switch, the fourth switch, and the inductor, a second capacitor whose first end is connected to a connection node of the second switch and the third switch, and a controller that controls switching on and off of the first to fourth switches. In at least one of a first pair configured with the first switch and the third switch and a second pair configured with the second switch and the fourth switch, the controller shifts a timing of switching from off to on between two switches.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 17/071,041, filed on Oct. 15, 2020, which claimspriority benefit of Japanese Patent Application No. JP 2019-191476 filedin the Japan Patent Office on Oct. 18, 2019. Each of theabove-referenced applications is hereby incorporated herein by referencein its entirety.

BACKGROUND

The present disclosure relates to a switching power supply device thatsteps down an input voltage to an output voltage.

In recent years, development of a switching power supply device having aconfiguration in which a switched capacitor and a direct current/directcurrent (DC/DC) converter including an inductor are combined with eachother has vigorously been conducted (e.g., refer to U.S. Pat. No.7,696,735 (FIG. 4)). Since the switching power supply device having thisconfiguration can suppress a voltage applied to a switch to be low, aswitching loss can be reduced, and efficiency can be enhanced.

SUMMARY

However, in a switching power supply device disclosed in U.S. Pat. No.7,696,735, noise that is likely to affect the outside of the switchingpower supply device is generated. This is because two switchesconfiguring a first pair are simultaneously switched from off to on at afirst timing and two other switches configuring a second pair aresimultaneously switched from off to on at a second timing.

In view of the above situation, it is desirable to suppress generationof noise that is likely to affect the outside of a switching powersupply device.

A switching power supply device disclosed in the present specificationis a switching power supply device that steps down an input voltage toan output voltage, and employs a configuration (first configuration) inwhich the switching power supply device includes a first switch whosefirst end is allowed to be connected to an applying end of the inputvoltage, a first capacitor, a second switch whose first end is allowedto be connected to a second end of the first switch and a first end ofthe first capacitor, a second capacitor, a third switch whose first endis allowed to be connected to a second end of the second switch and afirst end of the second capacitor, an inductor, a fourth switch whosefirst end is allowed to be connected to a second end of the thirdswitch, a second end of the first capacitor, and a first end of theinductor, and a controller that controls switching on and off of thefirst switch, the second switch, the third switch, and the fourthswitch. In at least one of a first pair configured with the first switchand the third switch and a second pair configured with the second switchand the fourth switch, the controller shifts a timing of switching fromoff to on between two switches. In a case where a timing of switchingfrom off to on is shifted between the first switch and the third switchin the first pair, the third switch is switched from off to on, andthen, the first switch is switched from off to on while the third switchis kept turned on. In a case where a timing of switching from off to onis shifted between the second switch and the fourth switch in the secondpair, the fourth switch is switched from off to on, and then, the secondswitch is switched from off to on while the fourth switch is kept turnedon.

In the switching power supply device having the first configuration, aconfiguration (second configuration) may be employed in which thecontroller shifts the timing of switching from off to on between thefirst switch and the third switch in the first pair and generates afirst switch control signal for controlling the first switch and a thirdswitch control signal for controlling the third switch; and a slew rateof the first switch control signal at a timing of switching the firstswitch from off to on is smaller than a slew rate of the third switchcontrol signal at a timing of switching the third switch from off to on.

In the switching power supply device having the first or secondconfiguration, a configuration (third configuration) may be employed inwhich the controller shifts the timing of switching from off to onbetween the second switch and the fourth switch in the second pair andgenerates a second switch control signal for controlling the secondswitch and a fourth switch control signal for controlling the fourthswitch; and a slew rate of the second switch control signal at a timingof switching the second switch from off to on is smaller than a slewrate of the fourth switch control signal at a timing of switching thefourth switch from off to on.

A switch control device disclosed in the present specification is aswitch control device that controls switching on and off of a firstswitch whose first end is allowed to be connected to an applying end ofan input voltage, switching on and off of a second switch whose firstend is allowed to be connected to a second end of the first switch and afirst end of a first capacitor, switching on and off of a third switchwhose first end is allowed to be connected to a second end of the secondswitch and a first end of a second capacitor, and switching on and offof a fourth switch whose first end is allowed to be connected to asecond end of the third switch, a second end of the first capacitor, anda first end of an inductor. The switching control device has aconfiguration (fourth configuration) in which, in at least one of afirst pair configured with the first switch and the third switch and asecond pair configured with the second switch and the fourth switch, atiming of switching from off to on is shifted between two switches. In acase where a timing of switching from off to on is shifted between thefirst switch and the third switch in the first pair, the third switch isswitched from off to on, and then, the first switch is switched from offto on while the third switch is kept turned on. In a case where a timingof switching from off to on is shifted between the second switch and thefourth switch in the second pair, the fourth switch is switched from offto on, and then, the second switch is switched from off to on while thefourth switch is kept turned on.

An in-vehicle device disclosed in the present specification has aconfiguration (fifth configuration) including the switching power supplydevice of any one of the first to third configurations or the switchcontrol device of the fourth configuration.

A vehicle disclosed in the present specification has a configuration(sixth configuration) including the in-vehicle device of the fifthconfiguration and a battery that supplies power to the in-vehicledevice.

The present disclosure can suppress generation of noise that is likelyto affect the outside of a switching power supply device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrating a configuration example of a switchingpower supply device;

FIG. 1B is a diagram illustrating a state of the switching power supplydevice immediately before a third timing;

FIG. 1C is a diagram illustrating the state of the switching powersupply device immediately before a sixth timing;

FIG. 2 is a timing chart illustrating an operation of a switching powersupply device according to an exemplary embodiment;

FIG. 3 is a timing chart illustrating an operation of a switching powersupply device according to a reference example;

FIG. 4 is a diagram illustrating a schematic configuration example of acontroller;

FIG. 5 is a timing chart illustrating respective currents flowingthrough an inductor and first to fourth switches; and

FIG. 6 is an external appearance view illustrating a configurationexample of a vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 1. ConfigurationExample of Switching Power Supply Device

FIG. 1A is a diagram illustrating a configuration example of a switchingpower supply device. A switching power supply device 1 illustrated inFIG. 1A is a switching power supply device that steps down an inputvoltage VIN to an output voltage VOUT, and includes a controller CNT1,first to fourth switches SW1 to SW4, a first capacitor CFLY, a secondcapacitor CMID, an inductor L1, an output capacitor COUT, and an outputfeedback unit FB1.

The controller CNT1 controls switching on and off of the first to fourthswitches SW1 to SW4, based on an output of the output feedback unit FB1.In other words, the controller CNT1 is a switch control device thatcontrols switching on and off of the first to fourth switches SW1 toSW4.

A first end of the first switch SW1 is connected to an applying end ofthe input voltage VIN. A second end of the first switch SW1 is connectedto a first end of the second switch SW2 and a first end of the firstcapacitor CFLY. As the first switch SW1, for example, a P-channel typemetal oxide semiconductor (MOS) transistor or an N-channel type MOStransistor can be used. For example, in a case where the N-channel typeMOS transistor is used as the first switch SW1, in order to generate avoltage higher than the input voltage VIN, the switching power supplydevice 1 may be provided with, for example, a bootstrap circuit.

A second end of the second switch SW2 is connected to a first end of thethird switch SW3 and a first end of the second capacitor CMID. As thesecond switch SW2, for example, the P-channel type MOS transistor or theN-channel type MOS transistor can be used. For example, in a case wherethe N-channel type MOS transistor is used as the second switch SW2, inorder to generate a voltage higher than a voltage VSWH at a connectionnode of the first switch SW1 and the second switch SW2, the switchingpower supply device 1 may be provided with, for example, the bootstrapcircuit.

A second end of the third switch SW3 is connected to a first end of thefourth switch SW4, a second end of the first capacitor CFLY, and a firstend of the inductor L1. As the third switch SW3, for example, theP-channel type MOS transistor or the N-channel type MOS transistor canbe used. For example, in a case where the N-channel type MOS transistoris used as the third switch SW3, in order to generate a voltage higherthan a voltage at a connection node of the second switch SW2 and thethird switch SW3, the switching power supply device 1 may be providedwith, for example, the bootstrap circuit.

A second end of the fourth switch SW4 is connected to ground potential.As the fourth switch SW4, the P-channel type MOS transistor or theN-channel type MOS transistor can be used, for example. Note that,unlike the present exemplary embodiment, the second end of the fourthswitch SW4 may be connected to an applying end of a voltage that islower than the input voltage VIN and is other than the ground potential.

The second end of the second capacitor CMID is connected to the groundpotential. Note that, unlike the present exemplary embodiment, thesecond end of the second capacitor CMID may be connected to the applyingend of the voltage that is lower than the input voltage VIN and is otherthan the ground potential. For example, the second end of the secondcapacitor CMID may be connected to a connection node of the inductor L1and the output capacitor COUT.

A second end of the inductor L1 is connected to a first end of theoutput capacitor COUT and an applying end of the output voltage VOUT.The applying end of the output voltage VOUT is connected with the loadLD1.

A second end of the output capacitor COUT is connected to the groundpotential. Note that, when ripples in the output voltage VOUT satisfyrequirement specifications even without the output capacitor COUT, aconfiguration provided with no output capacitor COUT may be used.

The output feedback unit FB1 generates and outputs a feedback signalaccording to the output voltage VOUT. As the output feedback unit FB1,for example, a resistance voltage-dividing circuit thatresistance-divides the output voltage VOUT and generates the feedbacksignal may be used. Further, for example, the output feedback unit FB1may be configured to obtain the output voltage VOUT and output theoutput voltage VOUT itself as the feedback signal. Note that the outputfeedback unit FB1 may be configured to also generate and output afeedback signal according to a current flowing through the inductor L1(hereinafter, referred to as an “inductor current IL”), in addition tothe feedback signal according to the output voltage VOUT. When theoutput feedback unit FB1 also generates the feedback signal according tothe inductor current IL, current mode control can be performed.

2. Operation of Switching Power Supply Device

FIG. 2 is a timing chart illustrating an operation of the switchingpower supply device 1, that is, an operation of the switching powersupply device according to the exemplary embodiment. FIG. 3 is a timingchart illustrating an operation of the switching power supply device 1in a case where the controller CNT1 performs control similar to that ofU.S. Pat. No. 7,696,735, that is, an operation of a switching powersupply device according to a reference example.

In FIGS. 2 and 3, Sk is a k-th switch control signal for controlling ak-th switch SWk. Note that k is an integer of one to four. Each of FIGS.2 and 3 illustrates a waveform of the k-th switch control signal Sk in acase where the first to fourth switches SW1 to SW4 are the NMOStransistors.

The controller CNT1 generates the k-th switch control signal Sk based onan output of the output feedback unit FB1. The controller CNT1 alsogenerates a k-th switch drive signal Gk configured so as to enhance acurrent capability of the k-th switch control signal Sk. The controllerCNT1 includes a control signal generator GNR1 and a driver DRVk asillustrated in FIG. 4, for example. The driver DRVk generates the k-thswitch drive signal Gk based on the k-th switch control signal Sk. Notethat the k-th switch drive signal Gk turns to a high level when the k-thswitch control signal Sk is a high level, and turns to a low level whenthe k-th switch control signal Sk is a low level. The k-th switch drivesignal Gk is supplied to a control end of the k-th switch SWk (a gate ofthe NMOS transistor when the k-th switch SWk is the NMOS transistor).

2-1. Control of First and Third Switches 2-1-1. Exemplary Embodiment

As illustrated in FIG. 2, in the exemplary embodiment, after a firsttiming t1 at which the second switch SW2 and the fourth switch SW4 areswitched from on to off, the controller CNT1 first switches the thirdswitch SW3 from off to on at a second timing t2. A period from the firsttiming t1 to the second timing t2 is what is generally called a deadtime period.

When the third switch SW3 is turned on, a current flows from the secondcapacitor CMID to the third switch SW3. This charges parasiticcapacitance PC1 connected to a connection node of the third switch SW3and the fourth switch SW4 (parasitic capacitance mainly formed betweenboth ends of the fourth switch), and a voltage VSW at the connectionnode of the third switch SW3 and the fourth switch SW4 increases. Sincea charged amount of the first capacitor CFLY is not changed, a voltageVSWH also increases as the voltage VSW increases. The voltage VSWHincreases until the voltage VSWH turns to be substantially the same asthe input voltage VIN.

During a short period of time after the timing t2, a spike current flowsthrough the third switch SW3. However, due to a circuit operation,although a withstand voltage of the first switch SW1 is to be more thanthe input voltage VIN, a withstand voltage of the third switch SW3 isonly required to be equal to or more than a half of the input voltageVIN. Accordingly, in the exemplary embodiment, on-resistance of thethird switch SW3 is easily reduced, and a switching loss of the thirdswitch SW3 can easily be reduced.

The above-described spike current flows from the second capacitor CMIDto the third switch SW3 and acts as a charging current of the parasiticcapacitance PC1. Since the first switch SW1 is turned off until a thirdtiming t3 to be described later arrives, the above-described spikecurrent does not affect a power supply line to which the input voltageVIN is applied. Accordingly, the exemplary embodiment can suppresspropagation of noise through the power supply line to which the inputvoltage VIN is applied. In other words, the exemplary embodiment cansuppress generation of noise that is likely to affect the outside of theswitching power supply line.

After the voltage VSWH increases until the voltage VSWH turns to besubstantially the same as the input voltage VIN, the controller CNT1switches the first switch SW1 from off to on at the third timing t3.Immediately before the third timing t3, as illustrated in FIG. 1B, thethird switch SW3 is turned on, and the first switch SW1, the secondswitch SW2, and the fourth switch SW4 are turned off. Further,immediately before the third timing t3, as illustrated in FIG. 1B, eachof a both-end potential difference VCFLY of the first capacitor CFLY anda both-end potential difference VCMID of the second capacitor CMID issubstantially a half of the input voltage VIN (VIN/2). Thus, each of thevoltage VMID at the connection node of the second switch SW2 and thethird switch SW3 and the voltage VSW at the connection node of the thirdswitch SW3 and the fourth switch SW4 turns to be substantially the sameas the half of the input voltage VIN (VIN/2). Further, immediatelybefore the third timing t3, as illustrated in FIG. 1B, a voltage VSWH ata connection node of the first switch SW1 and the second switch SW2 issubstantially the same as the input voltage VIN. Accordingly, a both-endpotential difference of the first switch SW1 at the third timing t3 issubstantially zero. As a result, a switching loss of the first switchSW1 at the third timing t3 is substantially zero.

The controller CNT1 then switches the first switch SW1 and the thirdswitch SW3 from on to off at a fourth timing t4.

The inductor current IL flows only through the third switch SW3 during aperiod from the second timing t2 to the third timing t3, and flowsthrough the first switch SW1 and the third switch SW3 while beingdistributed during a period from the third timing t3 to the fourthtiming t4. During a period from the second timing t2 to the fourthtiming t4, the inductor current IL increases.

In the present exemplary embodiment, a slew rate of the first switchcontrol signal S1 at the third timing t3 is set smaller than a slew rateof the third switch control signal S3 at the second timing t2. This canavoid the current flowing through the first switch SW1 at the thirdtiming t3 from increasing rapidly, and thus, switching noise of thefirst switch SW1 can be suppressed. In this manner, even when the firstswitch SW1 is slowly switched from off to on, the switching loss of thefirst switch SW1 at the third timing t3 is substantially zero asdescribed above, whereby efficiency is not deteriorated.

2-1-2. Reference Example

As illustrated in FIG. 3, in a reference example, after the first timingt1 at which the second switch SW2 and the fourth switch SW4 are switchedfrom on to off, the controller CNT1 switches the first switch SW1 andthe third switch SW3 from off to on at the second timing t2.

When the first switch SW1 and the third switch SW3 are turned on, acurrent flows from the first switch SW1 to the first capacitor CFLY, anda current flows from the second capacitor CMID to the third switch SW3.With this configuration, the parasitic capacitance PC1 is charged, andthe voltage VSW at the connection node of the first switch SW1 and thesecond switch SW2 increases.

During a short period of time after the second timing t2, a spikecurrent flows through both the first switch SW1 and the third switchSW3.

Further, the first end of the first switch SW1 is connected to theapplying end of the input voltage VIN, and thus, the spike currentflowing through the first switch SW1 affects the power supply line towhich the input voltage VIN is applied. Accordingly, the referenceexample finds it difficult to suppress propagation of the noise throughthe power supply line to which the input voltage VIN is applied. Inother words, the reference example finds it difficult to suppressgeneration of the noise that is likely to affect the outside of theswitching power supply device.

Further, in the reference example, the first switch SW1 is switched fromoff to on in a state in which the both-end potential difference of thefirst switch SW1 is not substantially zero, whereby the efficiency isalso deteriorated.

Further, the controller CNT1 switches the first switch SW1 and the thirdswitch SW3 from on to off at the fourth timing t4.

The inductor current IL flows through the first switch SW1 and the thirdswitch SW3 while being distributed during a period from the third timingt3 to the fourth timing t4. During the period from the second timing t2to the fourth timing t4, the inductor current IL increases.

2-2. Control of Second and Fourth Switches 2-2-1. Exemplary Embodiment

As illustrated in FIG. 2, in the exemplary embodiment, after the fourthtiming t4 at which the first switch SW1 and the third switch SW3 areswitched from on to off, the controller CNT1 first switches the fourthswitch SW4 from off to on at a fifth timing t5. A period from the fourthtiming t4 to the fifth timing t5 is what is generally called a dead timeperiod.

When the fourth switch SW4 is turned on, a current flows from the groundpotential to the inductor L1 through the fourth switch SW4. The secondswitch SW2 is turned off until a sixth timing t6 arrives, whereby nocurrent flows from the first capacitor CFLY to the second capacitorCMID. Accordingly, during a period from the fifth timing t5 to the sixthtiming t6, the current flowing through the fourth switch SW4 is equal tothe inductor current IL.

The controller CNT1 switches the second switch SW2 from off to on at thesixth timing t6. This short-circuits the first end of the firstcapacitor CFLY and the first end of the second capacitor CMID.Immediately before the sixth timing t6, as illustrated in FIG. 1C, thefourth switch SW4 is turned on, and the first switch SW1, the secondswitch SW2, and the third switch SW3 are turned off. Further, during theperiod from the third timing t3 to the fourth timing t4, the firstcapacitor CFLY is charged, whereby the both-end potential differenceVCFLY of the first capacitor CFLY increases. Further, the secondcapacitor CMID has been discharged, whereby the both-end potentialdifference VCMID of the second capacitor CMID decreases. As a result,immediately before the sixth timing t6, as illustrated in FIG. 1C, theboth-end potential difference VCFLY of the first capacitor CFLY ishigher than the half of the input voltage VIN (VIN/2), and the both-endpotential difference VCMID of the second capacitor CMID is lower thanthe half of the input voltage VIN (VIN/2). In other words, immediatelybefore the sixth timing t6, as illustrated in FIG. 1C, the voltage VSWHat the connection node of the first switch SW1 and the second switch SW2is higher than the half of the input voltage VIN (VIN/2), and thevoltage VMID at the connection node of the second switch SW2 and thethird switch SW3 is lower than the half of the input voltage VIN(VIN/2). Accordingly, at the sixth timing t6, when the second switch SW2is switched from off to on and the first end of the first capacitor CFLYand the first end of the second capacitor CMID are short-circuited, acurrent flows from the first end of the first capacitor CFLY toward thesecond capacitor CMID.

As a result, during a period from the sixth timing t6 to the firsttiming t1 in a next cycle, the current flowing through the fourth switchSW4 turns to be a sum of the inductor current IL and the current flowingfrom the first end of the first capacitor CFLY toward the secondcapacitor CMID.

During a period from the fifth timing t5 to the first timing t1 in thenext cycle, the inductor current IL decreases. Accordingly, at the sixthtiming t6, the inductor current IL is smaller than that at the fifthtiming t5. This can suppress the spike current flowing through thefourth switch SW4 when the fourth switch SW4 is switched from off to on,and thus, the switching noise of the fourth switch SW4 can be reduced.

The spike current flowing through the fourth switch SW4 does not affectthe power supply line to which the input voltage VIN is applied.However, among respective spike currents flowing through the first tofourth switches SW1 to SW4, the spike current flowing through the fourthswitch SW4 is the largest (refer to FIG. 5). Thus, even if the switchingnoise of the fourth switch SW4 does not propagate through the powersupply line to which the input voltage VIN is applied, the switchingnoise of the fourth switch SW4 may affect the outside of the switchingpower supply device while acting as radiation noise. In other words, inthe exemplary embodiment, by reducing the switching noise of the fourthswitch SW4, generation of the noise that is likely to affect the outsideof the switching power supply device can be suppressed. Note that, FIG.5 illustrates the inductor current IL and the currents ISW1 to ISW4respectively flowing through the first to fourth switches SW1 to SW4 inthe present exemplary embodiment. In FIG. 5, A denotes the maximum valueof the inductor current IL.

In the present exemplary embodiment, a slew rate of the second switchcontrol signal S2 at the sixth timing t6 is set smaller than a slew rateof the fourth switch control signal S4 at the fifth timing t5. This canavoid the current flowing through the second switch SW2 at the sixthtiming t6 from rapidly increasing, and thus, switching noise of thesecond switch SW2 can be suppressed.

2-2-2. Reference Example

As illustrated in FIG. 3, in the reference example, after the fourthtiming t4 at which the first switch SW1 and the third switch SW3 areswitched from on to off, the controller CNT1 switches the second switchSW2 and the fourth switch SW4 from off to on at the fifth timing t5.

When the second switch SW2 and the fourth switch SW4 are turned on, thecurrent flowing through the fourth switch SW4 turns to be the sum of theinductor current IL and the current flowing from the first end of thefirst capacitor CFLY toward the second capacitor CM ID. This increasesthe current flowing through the fourth switch SW4 when the fourth switchSW4 is switched from off to on, thereby increasing the switching noiseof the fourth switch SW4.

3. Application

Next, description will be made of an application example of theswitching power supply device 1 described above. FIG. 6 is an externalappearance view illustrating a configuration example of a vehiclemounting in-vehicle devices. A vehicle X in the present configurationexample mounts in-vehicle devices X11 to X17 and a battery (notillustrated) that supplies power to the in-vehicle devices X11 to X17.

The in-vehicle device X11 is an engine control unit that performscontrol related to an engine (e.g., injection control, electronicthrottle control, idling control, oxygen sensor heater control, andauto-cruise control).

The in-vehicle device X12 is a lamp control unit that performslighting-on/off control of, for example, a high intensity dischargedlamp (HID) or a daytime running lamp (DRL).

The in-vehicle device X13 is a transmission control unit that performscontrol related to a transmission.

The in-vehicle device X14 is a body control unit that performs controlrelated to motion of the vehicle X (e.g., anti-lock brake system (ABS)control, electronic power steering (EPS) control, and electronicsuspension control).

The in-vehicle device X15 is a security control unit that performsdriving control of, for example, a door lock and a crime preventionalarm.

The in-vehicle device X16 is an electronic device embedded in thevehicle X at a factory shipping stage as a standard accessory or afactory-installed option accessory, such as a wiper, anelectrically-controlled outside mirror, an automatic window, anelectrically-controlled sliding roof, a power seat, and an airconditioner.

The in-vehicle device X17 is an electronic device optionally mounted onthe vehicle X by a user, such as an in-vehicle audio/visual (A/V)device, a car navigation system, and an electronic toll collectionsystem (ETC).

Note that the switching power supply device 1 described above can beembedded in any of the in-vehicle devices X11 to X17.

4. Notes

It should be noted that, in addition to the above-described exemplaryembodiment, a configuration of the present disclosure can variously bemodified without departing from the gist of the disclosure. It should beconsidered that the above-described exemplary embodiment is illustrativein all aspects and is not limitative. It should be understood that thetechnical range of the present disclosure is given, not by thedescription of the above-described exemplary embodiment, but by thescope of the claims, and all modifications belonging to meanings andranges of the claims and equivalents are involved.

For example, in the above-described exemplary embodiment, in the firstpair configured with the first switch SW1 and the third switch SW3, thecontroller CNT1 shifts the timing for switching from off to on betweentwo switches (the first switch SW1 and the third switch SW3), while inthe second pair configured with the second switch SW2 and the fourthswitch SW4, the controller CNT1 shifts the timing for switching from offto on between two switches (the second switch SW2 and the fourth switchSW4). However, the present disclosure is not limited to such control.

In the first pair configured with the first switch SW1 and the thirdswitch SW3, the controller CNT1 may shift the timing for switching fromoff to on between two switches (the first switch SW1 and the thirdswitch SW3) while, in the second pair configured with the second switchSW2 and the fourth switch SW4, the controller CNT1 may not shift thetiming for switching from off to on between two switches (the secondswitch SW2 and the fourth switch SW4). In contrast, in the first pairconfigured with the first switch SW1 and the third switch SW3, thecontroller CNT1 may not shift the timing for switching from off to onbetween two switches (the first switch SW1 and the third switch SW3)while, in the second pair configured with the second switch SW2 and thefourth switch SW4, the controller CNT1 may shift the timing forswitching from off to on between two switches (the second switch SW2 andthe fourth switch SW4).

Alternatively, unlike the above-described exemplary embodiment, the slewrate of the first switch control signal S1 at the third timing t3 maynot be smaller than the slew rate of the third switch control signal S3at the second timing t2.

Alternatively, unlike the above-described exemplary embodiment, the slewrate of the second switch control signal S2 at the sixth timing t6 maynot be smaller than the slew rate of the fourth switch control signal S4at the fifth timing t5.

Alternatively, how to set the third timing t3 is not particularlylimited. For example, a setting value indicating a length of the periodfrom the second timing t2 to the third timing t3 may be stored in aninternal memory or an internal register in the controller CNT1 inadvance, and the controller CNT1 may switch the first switch SW1 fromoff to on based on the setting value. Alternatively, for example, thecontroller CNT1 may detect a voltage obtained by subtracting the voltageVSW from a third switch drive signal G3, and may switch the first switchSW1 from off to on when the voltage obtained by subtracting the voltageVSW from the third switch drive signal G3 exceeds a predetermined value(a value equal to or more than a threshold voltage of the NMOStransistor used as the third switch SW3 but equal to or less than thehalf of the input voltage VIN).

Alternatively, how to set the sixth timing t6 is not particularlylimited. For example, a setting value indicating a length of the periodfrom the fifth timing t5 to the sixth timing t6 may be stored in theinternal memory or the internal register in the controller CNT1 inadvance, and the controller CNT1 may switch the second switch SW2 fromoff to on based on the setting value. Alternatively, for example, thecontroller CNT1 may detect a voltage obtained by subtracting a groundvoltage from a fourth switch drive signal G4, and may switch the firstswitch SW1 from off to on when the voltage obtained by subtracting theground voltage from the fourth switch drive signal G4 exceeds apredetermined value (a value equal to or more than a threshold voltageof the NMOS transistor used as the fourth switch SW4 but equal to orless than the half of the input voltage VIN).

Alternatively, unlike the above-described exemplary embodiment, thefourth switch SW4 may be a diode. In a case where the fourth switch SW4is the diode, the controller CNT1 controls switching on/off of the firstto third switches SW1 to SW3 to control a bias voltage applied to thefourth switch SW4 (diode). Switching on/off of the fourth switch SW4(diode) is determined by the bias voltage applied to the fourth switchSW4 (diode). Thus, the controller CNT1 indirectly controls switchingon/off of the fourth switch SW4 (diode).

The present disclosure can be used for a step-down type switching powersupply device used in all fields (e.g., a home electric appliance field,an automotive field, and an industrial machinery field).

What is claimed is:
 1. A switching power supply device that steps downan input voltage to an output voltage, the switching power supply devicecomprising: a first switch whose first end is allowed to be connected toan applying end of the input voltage; a first capacitor; a second switchwhose first end is allowed to be connected to a second end of the firstswitch and a first end of the first capacitor; a second capacitor; athird switch whose first end is allowed to be connected to a second endof the second switch and a first end of the second capacitor; aninductor; a fourth switch whose first end is allowed to be connected toa second end of the third switch, a second end of the first capacitor,and a first end of the inductor; and a controller that controlsswitching on and off of the first switch, the second switch, the thirdswitch, and the fourth switch, wherein, in at least one of a first pairconfigured with the first switch and the third switch and a second pairconfigured with the second switch and the fourth switch, the controllershifts a timing of switching from off to on between two switches, in acase where a timing of switching from off to on is shifted between thefirst switch and the third switch in the first pair, the controllerswitches the third switch from off to on, and then switches the firstswitch from off to on while the third switch is kept turned on, and in acase where a timing of switching from off to on is shifted between thesecond switch and the fourth switch in the second pair, the controllerswitches the fourth switch from off to on, and then switches the secondswitch from off to on while the fourth switch is kept turned on.
 2. Theswitching power supply device according to claim 1, wherein thecontroller shifts the timing of switching from off to on between thefirst switch and the third switch in the first pair and generates afirst switch control signal for controlling the first switch and a thirdswitch control signal for controlling the third switch, and a slew rateof the first switch control signal at a timing of switching the firstswitch from off to on is smaller than a slew rate of the third switchcontrol signal at a timing of switching the third switch from off to on.3. The switching power supply device according to claim 1, wherein thecontroller shifts the timing of switching from off to on between thesecond switch and the fourth switch in the second pair and generates asecond switch control signal for controlling the second switch and afourth switch control signal for controlling the fourth switch, and aslew rate of the second switch control signal at a timing of switchingthe second switch from off to on is smaller than a slew rate of thefourth switch control signal at a timing of switching the fourth switchfrom off to on.
 4. A switch control device that controls switching onand off of a first switch whose first end is allowed to be connected toan applying end of an input voltage, switching on and off of a secondswitch whose first end is allowed to be connected to a second end of thefirst switch and a first end of a first capacitor, switching on and offof a third switch whose first end is allowed to be connected to a secondend of the second switch and a first end of a second capacitor, andswitching on and off of a fourth switch whose first end is allowed to beconnected to a second end of the third switch, a second end of the firstcapacitor, and a first end of an inductor, wherein, in at least one of afirst pair configured with the first switch and the third switch and asecond pair configured with the second switch and the fourth switch, atiming of turning from off to on is shifted between two switches, in acase where a timing of switching from off to on is shifted between thefirst switch and the third switch in the first pair, the third switch isswitched from off to on, and then, the first switch is switched from offto on while the third switch is kept turned on, and in a case where atiming of switching from off to on is shifted between the second switchand the fourth switch in the second pair, the fourth switch is switchedfrom off to on, and then, the second switch is switched from off to onwhile the fourth switch is kept turned on.
 5. An in-vehicle devicecomprising: a switching power supply device that steps down an inputvoltage to an output voltage, the switching power supply deviceincluding a first switch whose first end is allowed to be connected toan applying end of the input voltage, a first capacitor, a second switchwhose first end is allowed to be connected to a second end of the firstswitch and a first end of the first capacitor, a second capacitor, athird switch whose first end is allowed to be connected to a second endof the second switch and a first end of the second capacitor, aninductor, a fourth switch whose first end is allowed to be connected toa second end of the third switch, a second end of the first capacitor,and a first end of the inductor, and a controller that controlsswitching on and off of the first switch, the second switch, the thirdswitch, and the fourth switch, wherein, in at least one of a first pairconfigured with the first switch and the third switch and a second pairconfigured with the second switch and the fourth switch, the controllershifts a timing of switching from off to on between two switches, in acase where a timing of switching from off to on is shifted between thefirst switch and the third switch in the first pair, the third switch isswitched from off to on, and then, the first switch is switched from offto on while the third switch is kept turned on, and in a case where atiming of switching from off to on is shifted between the second switchand the fourth switch in the second pair, the fourth switch is switchedfrom off to on, and then, the second switch is switched from off to onwhile the fourth switch is kept turned on.
 6. An in-vehicle devicecomprising: a switch control device that controls switching on and offof a first switch whose first end is allowed to be connected to anapplying end of an input voltage, switching on and off of a secondswitch whose first end is allowed to be connected to a second end of thefirst switch and a first end of a first capacitor, switching on and offof a third switch whose first end is allowed to be connected to a secondend of the second switch and a first end of a second capacitor, andswitching on and off of a fourth switch whose first end is allowed to beconnected to a second end of the third switch, a second end of the firstcapacitor, and a first end of an inductor, wherein, in at least one of afirst pair configured with the first switch and the third switch and asecond pair configured with the second switch and the fourth switch, atiming of turning from off to on is shifted between two switches, in acase where a timing of switching from off to on is shifted between thefirst switch and the third switch in the first pair, the third switch isswitched from off to on, and then, the first switch is switched from offto on while the third switch is kept turned on, and in a case where atiming of switching from off to on is shifted between the second switchand the fourth switch in the second pair, the fourth switch is switchedfrom off to on, and then, the second switch is switched from off to onwhile the fourth switch is kept turned on.
 7. A vehicle comprising: anin-vehicle device that includes a switching power supply device thatsteps down an input voltage to an output voltage, the switching powersupply device including a first switch whose first end is allowed to beconnected to an applying end of the input voltage, a first capacitor, asecond switch whose first end is allowed to be connected to a second endof the first switch and a first end of the first capacitor, a secondcapacitor, a third switch whose first end is allowed to be connected toa second end of the second switch and a first end of the secondcapacitor, an inductor, a fourth switch whose first end is allowed to beconnected to a second end of the third switch, a second end of the firstcapacitor, and a first end of the inductor, and a controller thatcontrols switching on and off of the first switch, the second switch,the third switch, and the fourth switch, wherein, in at least one of afirst pair configured with the first switch and the third switch and asecond pair configured with the second switch and the fourth switch, thecontroller shifts a timing of switching from off to on between twoswitches, in a case where a timing of switching from off to on isshifted between the first switch and the third switch in the first pair,the third switch is switched from off to on, and then, the first switchis switched from off to on while the third switch is kept turned on, andin a case where a timing of switching from off to on is shifted betweenthe second switch and the fourth switch in the second pair, the fourthswitch is switched from off to on, and then, the second switch isswitched from off to on while the fourth switch is kept turned on; and abattery that supplies power to the in-vehicle device.
 8. A vehiclecomprising: a switch control device that controls switching on and offof a first switch whose first end is allowed to be connected to anapplying end of an input voltage, switching on and off of a secondswitch whose first end is allowed to be connected to a second end of thefirst switch and a first end of a first capacitor, switching on and offof a third switch whose first end is allowed to be connected to a secondend of the second switch and a first end of a second capacitor, andswitching on and off of a fourth switch whose first end is allowed to beconnected to a second end of the third switch, a second end of the firstcapacitor, and a first end of an inductor, wherein, in at least one of afirst pair configured with the first switch and the third switch and asecond pair configured with the second switch and the fourth switch, atiming of turning from off to on is shifted between two switches, in acase where a timing of switching from off to on is shifted between thefirst switch and the third switch in the first pair, the third switch isswitched from off to on, and then, the first switch is switched from offto on while the third switch is kept turned on, and in a case where atiming of switching from off to on is shifted between the second switchand the fourth switch in the second pair, the fourth switch is switchedfrom off to on, and then, the second switch is switched from off to onwhile the fourth switch is kept turned on; and a battery that suppliespower to the in-vehicle device.